The present disclosure relates to a liquid crystal display (LCD) and, more particularly, to a common voltage generating circuit of an LCD.
Recently, as electronic devices have become lightweight and slim, display devices are also required to be lightweight and slim. In order to meet such requirements, a variety of flat panel displays are being rapidly developed and popularized to replace conventional cathode-ray tube (CRT) displays.
A liquid crystal display (LCD) is one of the flat panel displays mentioned above. In the LCD, a common electrode, a color filter, and alignment layer, and so on are formed on an upper substrate, whereas thin-film transistors, pixel electrodes, and alignment layer, and so on are formed on a lower substrate, and a liquid crystal material with dielectric anisotropy is injected between the alignment layer of the upper substrate and the alignment layer of the lower substrate. A predetermined voltage is applied to the pixel electrode and the common electrode to create a predetermined electric field, and the created electric field changes the orientations of the liquid crystal molecules to adjust the light transmittance of the liquid crystal, so that an image may be displayed.
The LCD is thin and light and, thus, is easy to miniaturize. In addition, the LCD has a low driving voltage and a low power consumption and can provide an image quality close to that of the CRT display. Therefore, the LCD is widely used in a variety of devices, such as mobile communications terminals, monitors and notebook computers. In particular, most of the mobile communication terminals, represented by mobile phones, use the LCD as a display device.
In general, the LCD is driven by applying a predetermined range of voltages to data lines, to which the liquid crystal can respond with the respect to a common voltage applied to the common electrode of the upper substrate. If the LCD continues to respond in only one direction, it is degraded in performance. In order to prevent such performance degradation, data voltages that are inverted with respect to the common voltage are applied to the data lines of the LCD.
The common voltage is one of the most important factors that determines the image quality of the LCD. In general, before the shipment of the LCD, the common voltage is adjusted to an optimal value and the optimal common voltage is stored in a register. The system including the LCD is then programmed for optimal display using the optimal common voltage value stored in the register.
The manufacturing environment of an LCD may change due to the movement or expansion of the manufacturing process line after the initial shipment stage. This process instability may change the optimal common voltage that determines the characteristics of the LCD. Typically, it is difficult to store the changed optimal common voltage in the register. The reason for this is that the system program must also be changed when the changed optimal common voltage is stored in the register. This causes a load on the implementation of the system including the LCD. What is therefore required is an approach to setting the common voltage automatically, without changing the system program.